The Open Systems Interconnection model (OSI model) is a product of the Open Systems Interconnection effort at the International Organization for Standardization. It is a way of sub-dividing a communication system into smaller parts called layers. A layer is a collection of conceptually similar functions that provide services to the layer above it and receives services from the layer below it. On each layer an instance provides services to the instances at the layer above and requests service from the layer below.
For example, a layer that provides error-free communications, across a network provides the path needed by applications above it, while it calls the next lower layer to send and receive packets that make up the contents of the path. Conceptually two instances at one layer are connected by a horizontal protocol connection on that layer.
In 1978, work on a layered model of network architecture was started and the International Organization for Standardization (ISO) began to develop its OSI framework architecture. OSI has two major components: an abstract model of networking, called the Basic Reference Model or seven-layer model, and a set of specific protocols. The standard documents that describe the OSI model can be freely downloaded from the ITU-T as the X.200-series of recommendations. A number of the protocol specifications are also available as part of the ITU-T X series. The equivalent ISO and ISO/IEC standards for the OSI model are available from ISO, but only some of them at no charge.
The concept of a 7-layer model was provided by the work of Charles Bachman, then of Honeywell. Various aspects of OSI design evolved from experiences with the ARPANET, the fledgling Internet, NPLNET, EIN, CYCLADES network and the work in IFIP WG6.1. The new design was documented in ISO 7498 and its various addenda. In this model, a networking system is divided into layers. Within each layer, one or more entities implement its functionality. Each entity interacts directly only with the layer immediately beneath it, and provides facilities for use by the layer above it.
Protocols enable an entity in one host to interact with a corresponding entity at the same layer in another host. Service definitions abstractly describe the functionality provided to an (N)-layer by an (N−1) layer, where N is one of the seven layers of protocols operating in the local host.
The OSI layers are the Physical Layer (Layer-1), the Data Link Layer (Layer-2), the Network Layer (Layer-3), the Transport Layer (Layer-4), the Session Layer (Layer-5), the Presentation Layer (Layer-6) and the Application Layer (Layer-7).
The Physical Layer or Layer-1 defines the electrical and physical specifications for devices. In particular, it defines the relationship between a device and a physical medium. This includes the layout of pins, voltages, cable specifications, hubs, repeaters, network adapters, host bus adapters, (HBAs used in storage area networks) and more. The Physical Layer can be contrasted with the functions of the Data Link Layer. The Physical Layer is concerned primarily with the interaction of a single device with a medium, whereas the Data Link Layer is concerned more with the interactions of multiple devices (i.e., at least two) with a shared medium. Standards such as RS-232 do use physical wires to control access to the medium.
The major functions and services performed by the Physical Layer, Layer-1, are: (1) establishment and termination of a connection to a communications medium; (2) participation in the process whereby the communication resources are effectively shared among multiple users. For example, contention resolution and flow control; and (3) modulation, or conversion between the representation of digital data in user equipment and the corresponding signals transmitted over a communications channel. These are signals operating over the physical cabling (such as copper and optical fiber) or over a radio link.
The Data Link Layer is Layer-2 of the seven-layer OSI model of computer networking. It corresponds to, or is part of the link layer of the TCP/IP reference model. The Data Link Layer is the protocol layer, which transfers data between adjacent network nodes in a wide area network or between nodes on the same local area network segment. The Data Link Layer provides the functional and procedural means to transfer data between network entities and might provide the means to detect and possibly correct errors that may occur in the Physical Layer. Examples of data link protocols are Ethernet for local area networks (multi-node), the Point-to-Point Protocol (PPP), HDLC and ADCCP for point-to-point (dual-node) connections.
The Data Link Layer, Layer-2, is concerned with local delivery of frames between devices on the same LAN. Data Link frames, as these protocol data units are called, do not cross the boundaries of a local network. Inter-network routing and global addressing are higher layer functions, allowing Data Link or Level-2 protocols to focus on local delivery, addressing, and media arbitration. In this way, the Data Link layer is analogous to a neighborhood traffic cop; it endeavors to arbitrate between parties contending for access to a medium. When devices attempt to use a medium simultaneously, frame collisions occur. Data Link protocols specify how devices detect and recover from such collisions. Further, Data Link protocols may provide mechanisms to reduce or prevent collisions.
A frame is the unit of transmission in a link layer protocol, and consists of a link-layer header followed by a packet. A data packet on the wire or frame consists of just a long string of binary 0s and 1s. A frame review on the actual physical wire would show Preamble and Start Frame Delimiter, in addition to the other data. These are required by all physical hardware. If a receiver is connected to the system in the middle of a frame transmission, it ignores the data until it detects a new frame synchronization sequence. However, Preamble and Start Frame Delimiters are not displayed by packet sniffing software because these bits are stripped away at OSI Layer-1 by the Ethernet adapter before being passed on to the OSI Layer-2 which is where packet sniffers collect their data from. There are OSI Physical Layer sniffers, which can capture and display the Preamble and Start Frame but they are expensive and mainly used to detect physical related problems. Examples of frames are Ethernet frames (maximum 1500 byte plus overhead), PPP frames and V.42 modem frames.
Delivery of frames by Layer-2 devices is affected through the use of unambiguous hardware addresses. A frame's header contains source and destination addresses that indicate which device originated the frame and which device is expected to receive and process it. In contrast to the hierarchical and routable addresses of the network layer (Layer-3), Layer-2 addresses are flat, meaning that no part of the address can be used to identify the logical or physical group to which the address belongs. This can be an important feature. The data link thus provides data transfer across the physical link. That transfer can be reliable or unreliable. Many data link protocols do not have acknowledgments of successful frame reception and acceptance, and some data link protocols might not even have any form of checksum to check for transmission errors. In those cases, higher-level protocols must provide flow control, error checking, and acknowledgments and retransmission.
In IEEE 802 local area networks, the services and protocols specified map to the lower two layers (Data Link and Physical) of the seven-layer OSI networking reference model. The IEEE 802 standards are restricted to networks carrying variable-size packets. In fact, IEEE 802 splits the OSI Data Link Layer-2 into two sub-layers named or described in more detail as the Media Access Control (MAC) and Logical Link Control (LLC) sublayers. This means that the IEEE 802.2 LLC protocol can be used with all of the IEEE 802 MAC layers, such as Ethernet, token ring, IEEE 802.11, etc., as well as with some non-802 MAC layers such as FDDI. Other Data Link Layer-2 protocols, such as HDLC, are specified to include both sublayers, although some other protocols, such as Cisco HDLC, use HDLC's low-level framing as a MAC layer in combination with a different LLC layer. In the ITU-T G.hn standard, which provides a way to create a high-speed (up to 1 Gigabit/s) Local area network using existing home wiring (power lines, phone lines and coaxial cables), the Data Link Layer is divided into three sub-layers (Application Protocol Convergence, APC; Logical Link Control, LLC; and Medium Access Control, MAC).
Within the semantics of the OSI network architecture, the Data Link Layer, Layer-2, protocols respond to service requests from the Network Layer, Layer-3, and they perform their function by issuing service requests to the Physical Layer, Layer 1.
The Network Layer, Layer-3, provides the functional and procedural means of transferring variable length data sequences from a source to a destination via one or more networks, while maintaining the quality of service requested by the Transport Layer. The Network Layer performs network routing functions, and might also perform fragmentation and reassembly, and report delivery errors. Routers operate at this layer—sending data throughout the extended network and making the Internet possible. This is a logical addressing scheme—values are chosen by the network engineer. The addressing scheme is hierarchical.
The Transport Layer, Layer-4, provides transparent transfer of data between end users, providing reliable data transfer services to the upper layers. The Transport Layer controls the reliability of a given link through flow control, segmentation/desegmentation, and error control. Some protocols are state and connection oriented. This means that the Transport Layer can keep track of the segments and retransmit those that fail. Although not developed under the OSI Reference Model and not strictly conforming to the OSI definition of the Transport Layer, typical examples of Layer 4 are the Transmission Control Protocol (TCP) and User datagram Protocol (UDP).
The Session Layer, Layer-5, controls the dialogues or connections between computers. It establishes, manages and terminates the connections between the local and remote application. It provides for full-duplex, half-duplex or simplex operation, and establishes check-pointing, adjournment, termination, and restart procedures. The OSI model made this layer responsible for graceful close of sessions, which is a property of the Transmission Control Protocol, and also for session check-pointing and recovery, which is not usually used in the Internet Protocol Suite. The Session Layer is commonly implemented explicitly in application environments that use remote procedure calls.
The Presentation Layer, Layer-6, establishes a context between Application Layer entities, in which the higher-layer entities can use different syntax and semantics, as long as the presentation service understands both and the mapping between them. The presentation service data units are then encapsulated into Session Protocol data units, and moved down the stack. This layer provides independence from differences in data representation (e.g., encryption) by translating from application to network format, and vice versa. The Presentation Layer, Layer-6, works to transform data into the form that the Application Layer can accept. Layer-6 formats and encrypts data to be sent across a network, providing freedom from compatibility problems. It is sometimes called the Syntax Layer.
The Application Layer, Layer-7, provides network process to application functions.
Ethernet, which is standardized by IEEE 802.3, was developed in 1980 and is a family of frame-based computer networking technologies for local area networks (LANs). The name came from the physical concept of the ether. It defines a number of wiring and signaling standards for the Physical Layer, Layer-1, OSI networking model, as well as a common addressing format and Media Access Control at the Data Link Layer.
Ethernet has become and continues to be the dominant Layer-2 digital communications technology. Internet Protocol (IP), which is standardized by the Internet Engineering Task Force (“IETF”), was developed in 1981 and has become the dominant Layer-3 digital communications technology.
The combination of the twisted-pair versions of ethernet for connecting end systems to the network, along with the fiber optic versions for site backbones, is the most widespread-wired LAN technology. It has been used from around 1980 to the present, largely replacing competing LAN standards such as token ring, FDDI and ARCNET.
Pseudo-wire is a collection of technologies, which create a Layer-2 connection across an underlying Layer-3 communications service. Pseudo-wire is the common term for any technology that provides an OSI Layer-1 (physical layer, i.e., “wire”) service over a Packet Switched Network (PSN). A Packet Switched Network is any combination of one or more Intranets and the Internet. The direct peer-to-peer Pseudo-wire services are limited because they require special firewall configurations to permit them to work in most public Internet networks.
A PSN-Tunnel is a software tunnel that carries a service such as a Pseudo-wire across a Packet Switched Network, PSN or any combination of one or more Intranets and the Internet.
In recent years, the telecommunications companies also known as “Telcos” or “Telcoms” have provided much of the Internet services. Particularly, Telco voice and data services have progressively consolidated to focus on providing Layer-3 IP based services. However, many Telcos are now offering a variety of Layer-2 Carrier Ethernet services; such as by way of example, Point-to-Point “LAN Extension” Services, Metro Ethernet Multi-Point-to-Multi-Point Services and even Global Ethernet Services.
Increasingly, many customers prefer to procure communications services as Layer-2 rather than as Layer-3 in order to achieve technical simplicity and greater security. When a Telco provides a Layer-3 service to a customer then the Telco and the customer have to fully co-operate on Layer-3 matters such as, for example without limitation, Layer-3 addressing plans (e.g., W addresses), Layer-3 routing protocols (e.g., OSPF and BGP), etc. This is cumbersome for both the Telco and the customer and if a customer uses many Telcos such Layer-3 co-operation can become onerous and unworkable.
When a Telco provides a Layer-2 service to a customer, then the Telco and the customer have requirements to co-operate albeit less than when providing a Layer-3 service, thus it is easier for both customer and Telco. Nonetheless, the adjacent layers are in communication one with the other, and such communication must be coordinated. Still further, when a Telco provides a Layer-3 service to a customer, then the Telco has access to the customer's Layer-3 network, which is a potential security risk. When a Telco provides a Layer-2 service to a customer, then the Telco has no access to the customer's Layer-3 network, thus it is easier for both customer and Telco.
The current Telco Layer-2 services are limited in two primary ways. First, the Telco Layer-2 services can only be provisioned across the Telco's core network and other networks with Telco-Telco Network-Network Interconnect (NNI) agreements. Second, the Telco usually takes 30-90 days to implement and integrate such additional Layer-2 services into existing Telco core network and other networks with Telco interconnect agreements. These arrangements make it difficult to provide services to sites that are not served by the Telco's own or interconnected infrastructure and make it difficult to provide services rapidly.
Another important issue with Telco Layer-3 network offerings is mismatched features and requirements between or among networks. For example, one carrier may support five different classes of service while another may support only three. Unless the carriers have the same number of classes of service, each with identical parameters, it is extremely difficult to translate services between carriers at the NNI in a way that meets the end customer's desired level of service from the carrier or carriers.
Other problems include mismatched inter-carrier logical and physical interfaces, transport methods, packet encapsulation, and the like. Unless both carriers agree on the physical media and the have such physical media available, then such inter-carrier logical and physical interfaces are incompatible.
These are only a few of the many and sundry problems that are associated with providing Telco services, generally, and Telco Layer-2 services, specifically. These are problems that have been present since the inception of providing Telco services. There has existed, and continues to exist, a huge need to provide such Telco services.
Further, the many and sundry problems exist in an industry with stellar, first-rate technical capabilities and personnel. Unfortunately, neither the stellar, first-rate technology nor the stellar, first-rate personnel have been able to solve the many problems associated with providing such services. To the contrary, as the demand for additional Telco services has risen, the problems associated with providing the services has exceed the demand. These problems are particularly acute at the fluid edge of the network, often referred to as “the last mile.” The edge of the network is contrasted with a core network, which refers to the high capacity communication facilities that connect primary nodes, rather than edge devices that provide entry points into service provider networks and/or the core network. Time is always of the essence with respect to conditions and locations at the edge of the network. There exists no likelihood of success with respect to solving the type of persistent problems herein discussed, and to achieve success over such problems is unexpected.
It is desirable to overcome the limitations of the current Telco Layer-2 and Layer-3 services and the limitations of Internet/firewall deployment.
It is, therefore, a feature of the present disclosure to provide a method and system for a Layer-2 Pseudo-wire rapid-deployment service over unknown Internet protocol networks.
Another feature of the present disclosure is to provide a method and system for the interconnection of disparate networks in a rapid and time efficient manner where the disparate networks are not served by a common Telco or are at locations that are not presently well served by the Telco. See, for example, FIG. 1 with respect to the “connection” between CE-A (102) and CE-B (202).
Yet another feature of the present disclosure is to provide a method and system that addresses the problem of rapid connectivity of an existing network to a new location or locations not presently served by a customer's incumbent Telco via a physical connection. See, for example, FIGS. 1 and 2 reference CE-A (102) and CE-B (202).
Yet still another feature of the present disclosure is to provide a method and system that offers almost instant Layer-2 connectivity over any available physical media (general Internet service via DSL, Satellite, Wireless and the like) between the locations (for example, CE-A and CE-B) in the interim period prior to the incumbent Telco's permanent connectivity solution whereby such deployments, even in major metropolitan locations, can take several months.
The above features of the present disclosure are of high value to industry and the problems are not well addressed, if at all, by existing solutions and methods.
Additional features and advantages of the disclosure will be set forth in part in the description which follows, and in part will become apparent from the description, or may be learned by practice of the method or system. The features and advantages of this disclosure may be realized by means of the combinations and steps particularly pointed out in the appended claims.